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  1. sjohns4

    Transformer Primary Voltage & Tap Changers

    Thanks all. The concept seemed too simple to actually work. Mike
  2. sjohns4

    Transformer Primary Voltage & Tap Changers

    I'm looking to possibly re-cover and re-use some 25 & 50 kVA single phase distribution transformers. We're a primary power customer on a 13.2kV / 7.6 kV system. The transformers are name plate 13200GRDY / 7600 HV and have 2x2.5% taps over and below nameplate. By my math, with the tap changer at...
  3. sjohns4

    Extreme Flow Variations & Process

    I took a look into RBC's, they do seem attractive. A lot of attached growth in a small footprint. Figured an Aqua-disk or similar on the effluent side. One of the membrane suppliers claimed they could provide a system to meet our needs. A couple things didn't quite smell right to me, care to...
  4. sjohns4

    Extreme Flow Variations & Process

    Yes, to about everything that was said. My knee jerk was a re-circulating sand filter or Orenco type plant. I used to put those in state parks for this exact reason. I knew they worked, but couldn't tell you why they could accommodate such varying loadings. The downside with either of those is...
  5. sjohns4

    Wastewater pumpstation ventilation/odour control

    I highly doubt you'll be able to passively vent the wet well. Any time I've seen an installation where we had to provide that kind of air flow there was some forced induction. Besides, it's the really low dry weather flow when everything is stagnant that's really causing the gas problem and...
  6. sjohns4

    Extreme Flow Variations & Process

    I'm preparing a PER for a training facility that sees incredibly variable flows. The variation will happen weekly. There can be intermittent periods of extremely high flows (~140,000 GPD) flowed by periods of extremely low flows (~8,000 GPD), and various levels between. I'm using 350 mg/l BOD &...
  7. sjohns4

    EPDM Membrane Diffuser Life?

    This is a conventional plug flow aeration basin, so aside from rare anomalies they're on 24-7. They're getting something of a calcium-iron scale and we're starting to see some failures. They were installed in 2010, so wondering if these are premature and any related to the buildup or if we've...
  8. sjohns4

    EPDM Membrane Diffuser Life?

    What sort of life span is typical for EPDM tube type membrane diffusers in municipal wastewater treatment plant applications? Thanks, Mike
  9. sjohns4

    IEC conductor and overcurrent protection sizing criteria?

    I'm working with a volunteer organization to provide training to a group of engineers in Rwanda. Their primary focus is to provide drinking water, but as most of us water people have had to learn along the way you need electricity to turn the pump. It's been well documented, and I observed...
  10. sjohns4

    Corner Grounded Delta 480 volt

    Code compliance aside, I've seen new equipment installed in a facility with a corner grounded delta. We did an upgrade at a plant that had a corner grounded delta service. We didn't add a transfer switch however; but there were existing generators and transfer switches present that were much...
  11. sjohns4

    Single Phase Inrush & Generator?

    This is all great info guys. The team that's currently in country should be back in a week or so. With any luck they'll come back with a final well location. Once that happens, I confirm the hydraulics and pump size, I'll be back for assistance in working out the electrical details! Bill: Not...
  12. sjohns4

    Single Phase Inrush & Generator?

    OK, that makes good sense. It sounds as if the drive would switch to the braking resistor even, or primarily, in a "motor stop" state, correct? If we see a DC overvoltage condition due to no or light load on the panels, the VFD will pull the resistor in. I got that part. As soon as the...
  13. sjohns4

    Single Phase Inrush & Generator?

    "Crate it up and ship it to you"...are you kidding me? No way I'd pass up the chance to play with solar panels and VFD's!!! Seriously though, thanks for the offer! Re: Cable length - The campus and proposed tank site is located approximately 3,000 linear feet from the proposed well site. It's...
  14. sjohns4

    Single Phase Inrush & Generator?

    The generator was the primary reason I was trying to keep pump run times low as I figured the motor was the biggest wear item not to mention the locals may get tired of days filled with engine noise. It makes sense the inrush current could be problematic for extremely long cable runs. Off the...
  15. sjohns4

    Single Phase Inrush & Generator?

    I pulled the current draw from the pump manufacturer's cut sheet. I'm inclined to clamp the fluke on some of the local installations where, as typical, the motor should not be running anywhere near full load. May get back to you on that one (all would be 3-phase though). I thought, according to...
  16. sjohns4

    Single Phase Inrush & Generator?

    I'd say the building will probably be a necessary evil. Rather than size the wire for 125% FLA, I was thinking I'd use a current somewhere between FLA and actual Amps at the pump operating point to keep conductor size manageable / reasonable. I'd scratched out a scenario with a 20% boost and...
  17. sjohns4

    Single Phase Inrush & Generator?

    IeeeEEEeeye exactly! I figured our in house electrical engineer would trip an overload or go into melt down trying to figure this one out! Even a water/wastewater guy (me) knows we're committing too many sins to sleep well at night here! I'm committing a few hydraulically; but in a situation...
  18. sjohns4

    Single Phase Inrush & Generator?

    Cable length is a problem: The location where we may be drilling the well is at the bottom of the hill, the location where we need the water is on the top of a hill at least one ridge over. Total cable length is approaching 3,000 LF. With single phase DOL starting I was thinking of a...
  19. sjohns4

    Single Phase Inrush & Generator?

    Thanks guys. I figured capacitors would be too simple. I suppose a VFD of this size isn't terribly expensive and practically a commodity item now anyway? Any recommendations on the drive? I see a lot of AB and ABB in the water wastewater world. One of my concerns from the get go with a VFD is...
  20. sjohns4

    Single Phase Inrush & Generator?

    I'm working on a water supply project in Haiti. The pipes, pump, and tank are the easy parts. Our power source is going to be limited to a portable generator that operates 2-3 hours every couple of days. The submersible well pump I've selected is a of European manufacturer with approximately a...

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